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XXII. An Account of Experiments on the Reflecting Telescope . By the Right 
Honourable Lord Oxmantown, F.R.S., 8$c. 
Received May 9, — Read June 18, 1840. 
For several years I have been engaged in a series of experiments, in the hope of in- 
creasing the power of the telescope, and I am induced, perhaps rather prematurely, 
to lay some account of them before the Royal Society, conceiving that, from the scale 
upon which they have been carried on, and perhaps from their results, they may 
prove interesting, particularly to those who have devoted their attention to such sub- 
jects. I should have been glad to have postponed this communication to a more di- 
stant time, so as to have rendered it in many respects more complete, but as experi- 
ments on a large scale are necessarily very tedious (months, even years, passing away 
almost imperceptibly), to have done so would have been to have postponed it inde- 
finitely, and to have withheld facts which may perhaps be useful to those who are 
engaged in similar pursuits. 
All the experiments I am about to describe relate solely to the Reflecting Tele- 
scope. With the exception of a few trifling experiments many years ago on fluid 
object-glasses, which led to no result, I have not had any experience in the construc- 
tion of the refractor. 
I have long thought that in the present state of knowledge there was not much 
prospect of improving the refractor to any considerable extent ; the fluid object-glass, 
at least in my hands, did not appear promising, and the improvements which have 
been made in the manufacture of glass on the continent, seem to have effected little 
more than to afford the means of constructing larger discs of tolerably perfect glass, 
than was formerly practicable ; still wanting, however, that exact homogeneity, and 
indeed those optical properties essential to any great increase of power. Upon the 
whole, therefore, there seemed to me to be but little chance of effecting anything 
really important in the present state of astronomy, except by improving the reflecting 
telescope ; to that object, therefore, every effort was directed. The task was evidently 
a very difficult one, as the late Sir W. Herschel had apparently almost exhausted 
the subject, having devoted to it acquirements the most varied and extensive, and at 
the same time the most suitable, during a very long life. Still it did not seem im- 
possible that, profiting by his labours, and imitating his example of steady perseve- 
rance, some advance might be made, trifling perhaps, but eventually leading to valu- 
able results. 
The great object seemed to be, to remove, as far as possible, the causes, owing to 
